This invention relates to the preparation of ruthenium and osmium compounds, which are particularly useful as chemical vapor deposition precursors.
Films of metals and metal oxides, particularly ruthenium and osmium films and oxides thereof, are becoming important for a variety of electronic and electrochemical applications. For example, high quality RuO2 thin films deposited on silicon wafers have recently gained interest for use in ferroelectric memories. Ruthenium and osmium films are generally unreactive to silicon and metal oxides, resistant to diffusion of oxygen and silicon, and are good conductors. Oxides of these metals also possess these properties, although perhaps to a different extent.
Thus, films of ruthenium and osmium and oxides thereof have suitable properties for a variety of uses in integrated circuits. For example, they can be used in integrated circuits for electrical contacts. They are particularly suitable for use as barrier layers between the dielectric material and the silicon substrate in memory devices, such as ferroelectric memories. Furthermore, they may even be suitable as the plate (i.e., electrode) itself in capacitors.
There are a wide variety of ruthenium and osmium compounds that can be used as precursors for the preparation of such films. Many are particularly well suited for use in chemical vapor deposition techniques. See, for example, U.S. Pat. No. 5,372,849 (McCormick et al.), which discloses the use of ruthenium and osmium compounds containing carbonyl ligands and other ligands. Typically, such compounds can be prepared by the thermal or photolytic reaction of Ru3(CO)12 or Os3(CO)12 with a neutral two electron donor ligand in benzene. See, for example, Johnson et al., Nature, 901-902 (1967), and Cowles et al., Chem. Commun., 392 (1969). Although such reactions provide good yields (e.g., 80-90%), they require generally long reaction times (e.g., 4 days). Thus, there is a continuing need for methods for the preparation of such ruthenium and osmium compounds in high yields with shorter reaction times.
The present invention provides methods for the preparation of compounds of the formula (Formula I):
LyM(CO)z
wherein M is Ru or Os, each L is independently a neutral ligand, y=1-4, and z=1-5. These methods involve the reaction of Ru3(CO)12 or Os3(CO)12 with a neutral ligand in a solvent system having a boiling point higher than that of benzene at atmospheric pressure. The solvent system can include one solvent, such as toluene, xylene, substituted benzene, heptane, octane, nonane, or an azeotropic mixture. The azeotropic mixture can contain one or more solvents having a boiling point at atmospheric pressure higher than that of benzene.
Using methods of the present invention, the product yields are preferably higher than conventional methods, and the reaction times are shorter than conventional methods. Preferably, using the methods of the present invention, a complex of Formula I is prepared in greater than about 90% yield, more preferably, in greater than about 95% yield, and most preferably, in greater than about 99% yield. Preferably, using the methods of the present invention, a complex of Formula I is prepared in no greater than about 36 hours, and more preferably, in no greater than about 24 hours.